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Methylene Units (methylene + unit)

Distribution by Scientific Domains

Chemistry	90%

Selected Abstracts

Recognition of protonated aliphatic ,,,-diamines by coproporphyrin I tetraanion in water

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2002
Alejandro Flores-Villalobos
Abstract Interactions of aliphatic ,,,-diamines [H2N(CH2)nNH2, 2,,,n,,,8] with coproporphyrin I tetraanion (CP) were studied by spectrophotometry, fluorimetry and 1H NMR spectroscopy in the pH range 7,10 and ionic strengths 0.01,0.1,M. Diprotonated diammonium cations induce dimerization of CP by forming 1:1 complexes with CP which undergo much stronger self-aggregation than free CP tetraanions. On increasing the number of methylene units n connecting the ammonium groups, the binding constants for the complex formation with monomeric CP (KL) increase but the dimerization constants of the resulting complexes decrease. A hydrophobic contribution to the binding free energy of ,1.6,±,0.2,kJ,mol,1 per methylene unit was obtained from the linear correlation of logKL values extrapolated to zero ionic strength vs the number of methylene units (n,=,2,6). A model for diammonium-induced porphyrin dimerization is proposed, which involves complexation of diammonium cations with CP monomer via a combination of electrostatic and hydrophobic interactions and subsequent formation of porphyrin face-to-face dimers in which diammonium cations serve as the stabilizing bridges via ion pairing to carboxylate groups of two CP monomeric units. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Two similar dibenzo cyclic ethers with dissimilar conformations

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009
Dennis H. Burns
Two dibenzo cyclic ether compounds, 6,12-dibromodibenzo[d,i]-1,2,3,6,7,8-hexahydro-1,3-dioxecin (systematic name: 8,16-dibromo-2,4-dioxatricyclo[12.4.0.05,10]octadeca-5,7,9,14,16,18-hexaene), C16H14Br2O2, (II), and 8,14-dibromodibenzo[f,k]-1,5-dioxa-1,2,3,4,5,8,9,10-octahydrocyclododecene (systematic name: 7,19-dibromo-11,15-dioxatricyclo[14.4.0.05,10]icosa-5,7,9,16,18,20-hexaene), C18H18Br2O2, (III), were prepared as scaffolding for phosphate-anion receptors. In both compounds, the two aromatic rings are linked by three methylene units ortho to the oxygen substituent of each ring. The only difference between the two compounds is the number of methylene units linking the two ether O atoms. The dibenzo cyclic ether with an ether linkage of one methylene unit adopts a chair-like conformation, where the two aromatic rings are parallel to each other. On the other hand, the dibenzo cyclic ether with an oxygen linkage of three methylene units adopts a bowl-like conformation. The latter scaffold configuration is the only structure of the two that would allow for the placement of convergent functional groups necessary for the establishment of an anion-selective binding pocket. [source]

Structure,Activity Study on the Spatial Arrangement of the Third Aromatic Ring of Endomorphins 1 and 2 Using an Atypical Constrained C,Terminus

CHEMMEDCHEM, Issue 3 2007
Ye Yu Dr.
Abstract The discovery of endomorphins (EMs) has opened the possibility of searching for new analgesics. However, the design of peptide analgesics has proven to be very difficult as a result of their conformational flexibility and a lack of clarity in structure,activity relationships (SAR). In EMs, the amino acid side chains exhibit considerable conformational flexibility, especially in the third aromatic ring, which is free to adopt a bioactive conformation. To resolve these problems, a series of C,terminus EM analogues, [Xaa4 -R]EMs, modified through the substitution of Phe4 with nonaromatic residues and termination with benzyl groups, were designed to generate conformational constrains of the third aromatic ring by amide bond and torsion angles (,4 and ,4) of Xaa4. Introduction of (S)-,-methyl or (S)/(R)-,-carboxamide on the methylene unit of the benzyl group was designed to produce an atypical topographical constraint (,5) of the third aromatic ring rotation. Interestingly, some EM derivatives, with elimination of the C-terminal carboxamide group and significant changes in the address sequence (Phe4 -NH2), still exhibited higher ,-opioid receptor (MOR) affinity than unmodified EMs. In contrast, some analogues with incorrectly constrained C,termini displayed very low affinity and pharmacological activities. Thus, our results indicate that these EM analogues, with atypical constrained C,termini, provide model compounds with potent MOR agonism. They also give evidence that the proper spatial orientation and conformational restriction of the third aromatic ring are crucial for the interaction of EMs with MOR. [source]

Adsorption of 1,3-Benzenedithiol and 1,3-Benzenedimethanethiol on Gold Surfaces,

CHEMPHYSCHEM, Issue 12 2008
Jong Kuk Lim Dr.
Abstract The adsorption characteristics of 1,3-benzenedithiol (1,3-BDT) and 1,3-benzenedimethanethiol (1,3-BDMT) on Au surfaces are investigated by means of surface-enhanced Raman scattering, UV/Vis absorption spectroscopy, and cyclic voltammetry (CV). 1,3-BDMT is found to adsorb via two S,Au linkages at concentrations below monolayer coverage, but to have an upright geometry as the concentration increases on Au nanoparticles. On the other hand, 1,3-BDT is found to adsorb by forming two S,Au linkages, regardless of concentration, based on the disappearance of the ,(SH)free stretching band. Because of the absence of the methylene unit, 1,3-BDT appeares not to self-assemble efficiently on Au surfaces. The UV/Vis absorption spectroscopy and CV techniques are also applied to check the formation of self-assembled monolayers of 1,3-BDT and 1,3-BDMT on Au. Density functional theory calculations based on a simple adsorption model using an Au8 cluster are performed to better understand the nature of the adsorption characteristics of 1,3-BDT and 1,3-BDMT on Au surfaces. [source]

Recognition of protonated aliphatic ,,,-diamines by coproporphyrin I tetraanion in water

The effects of spacer length on the fluorescence quantum yields of the benzofurazan compounds bearing a donor,acceptor system

LUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 1 2002
Maki Onoda
Abstract We studied the effects of spacer length on the fluorescence quantum yields (,) of photoinduced electron transfer (PET) reagents, using nitrobenzoxadiazole (NBD) derivatives that have the ,NMe2 moiety and NBD,NH, fluorophore as electron donor (D) and electron acceptor (A), respectively. The , values were reduced as the spacer length became shorter (n,,,4; n is the number of methylene units of the spacer) and the fluorescence recovered by suppression of the PET process. It is necessary for the useful PET reagents to link D and A with a short spacer to obtain a difference in the , values between fluorescent ,off-state' and ,on-state'. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Crystallization kinetics of poly(trimethylene terephthalate)

POLYMER ENGINEERING & SCIENCE, Issue 2 2001
Hoe H. Chuah
The bulk isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) was studied using a differential scanning calorimeter. Avrami's theory was used to analyze the data. Based on crystallinity growth rate, Avrami rate constant, K, and crystallization half-time, PTT's crystallization rate is between those of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) when compared at the same degree of undercooling. PBT has the highest crystallization rate with K in the order of 10,2 to 10,1 min,n. It is about an order of magnitude faster than PTT at 10,3 to 10,2 min,n, which in turn is an order of magnitude faster than PET with K of 10,4 to 10,2 min,n. Contrary to previous reports (PTT was not included in the study) that aromatic polyesters with odd numbers of methylene units were more difficult to crystallize than the even-numbered polyesters, PTT did not fit in the prediction and did not follow the odd-even effect. [source]

Two similar dibenzo cyclic ethers with dissimilar conformations

Structure,Activity Relationships of SSAO/VAP-1 Arylalkylamine-Based Substrates

CHEMMEDCHEM, Issue 4 2009
Francesc Yraola Dr.
Abstract SSAO/VAP-1 substrates may be valuable for the treatment or prevention of diabetes mellitus, as they show insulin-mimetic properties. This review highlights the importance of studying the relevant steric and electronic features in the development of new ligands with better SSAO/VAP-1 recognition, enhanced selectivity over other amine oxidases, and improved metabolic behavior. Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) substrates show insulin-mimetic effects and are therefore potentially valuable molecules for the treatment of diabetes mellitus. Herein we review several structural and electronic aspects of SSAO arylalkylamine-based substrates. Two main modifications directly affect amine oxidase (AO) activity: 1),variation in ring substitution modulates the biological activity of the arylalkylamine ligand by converting a substrate into a substrate-like inhibitor, and 2),variation in the number of methylene units between the aromatic ring and the ammonium groups of the arylalkylamine substrates dramatically alters the oxidation rate between species. Furthermore, we review relevant information about mammalian SSAO/VAP-1 substrate selectivity and specificity over monoamine oxidases (MAOs). [source]

Synthesis of Aromatase Inhibitors and Dual Aromatase Steroid Sulfatase Inhibitors by Linking an Arylsulfamate Motif to 4-(4H -1,2,4-triazol-4-ylamino)benzonitrile: SAR, Crystal Structures, in,vitro and in,vivo Activities

CHEMMEDCHEM, Issue 11 2008
Christian Bubert Dr.
Abstract 4-(((4-Cyanophenyl)(4H -1,2,4-triazol-4-yl)amino)methyl)phenyl sulfamate (6,a) was the first dual aromatase,sulfatase inhibitor (DASI) reported. Several series of its derivatives with various linker systems between the steroid sulfatase (STS) and the aromatase inhibitory pharmacophores were synthesised and evaluated in JEG-3 cells. The X-ray crystal structures of the aromatase inhibitors, DASI precursors 42,d and 60, and DASI 43,h were determined. Nearly all derivatives show improved in,vitro aromatase inhibition over 6,a but decreased STS inhibition. The best aromatase inhibitor is 42,e (IC50=0.26,nM) and the best DASI is 43,e (IC50,aromatase=0.45,nM, IC50,STS=1200,nM). SAR for aromatase inhibition shows that compounds containing an alkylene- and thioether-based linker system are more potent than those that are ether-, sulfone-, or sulfonamide-based, and that the length of the linker has a limited effect on aromatase inhibition beyond two methylene units. Compounds 43,d,f were studied in,vivo (10,mg,kg,1, single, p.o.). The most potent DASI is 43,e, which inhibited PMSG-induced plasma estradiol levels by 92,% and liver STS activity by 98,% 3,h after dosing. These results further strengthen the concept of designing and developing DASIs for potential treatment of hormone-related cancers. [source]